1. Field of the Invention
The invention relates to an image signal processing device and, more particularly, to an image signal processing device for processing an image signal or a video signal containing a copy guard signal.
2. Description of Related Art
For copy guard requirements, a copy guard signal is typically inserted in an image signal output by a video output device such as a VCD or DVD player to thereby avoid the image signal from directly copying by a video recorder.
FIG. 1 is a schematic diagram of an image signal 1 containing a copy guard signal 125. As shown in FIG. 1, the image signal 1 includes horizontal synchronizing signals 111, 112, and a vertical retrace blanking period 12. The vertical retrace blanking period 12 further includes equalized pulse signals 121, 122, a vertical synchronizing signal 123 and a horizontal synchronizing signal 124. The copy guard signal 125 is inserted in the horizontal synchronizing signal 124.
The image signal 1 containing the copy guard signal 125 can be broadcasted on a typical display device such as a CRT TV, but not on a digital display device such as an LCD TV. Namely, the broadcasted frames cannot be viewed on the LCD TV.
To overcome this, FIG. 2 shows a solution as provided by U.S. Pat. No. 5,133,008 granted to Fujita for an “Image Signal Processing Device”. As shown in FIG. 2, the image signal processing device includes a horizontal synchronizing signal detector 21, a primary oscillator 22, a gate circuit 23, a counter 24 and an image signal processing circuit 25. As shown in FIG. 3, after vertical SYNC signals 31 are detected by the horizontal synchronizing signal detector 21, the counter 24 is reset and the primary oscillator 22 is triggered to produce a signal to indicate a coy guard signal generation section (referred to as an indicative signal 32), wherein the period of the indicative signal 32 is smaller than the vertical retrace blanking period 33. Meanwhile, the gate circuit 23 closes the output of horizontal SYNC signals for controlling the counter 24 not to count the number of the horizontal SYNC signals containing a coy guard signal. Namely, the gate circuit 23 outputs a replacing signal 34 to mask the horizontal SYNC signals containing the copy guard signal. An image signal can be viewed on a digital TV and thus the problem described above is solved.
Similarly, another solution is provided by U.S. Pat. No. 5,337,157 granted to Nakata for a “Copy Guard Processing Detecting Apparatus”, which requires a counter to count the number of horizontal synchronizing signals in an entire frame and a non-vertical retrace blanking period respectively. Subsequently, the difference of the number of horizontal synchronizing signals between the entire frame and the non-vertical retrace blanking period is used to determine whether a copy guard signal presents or not.
However, the two solutions require the counter for counting the number of scan lines in a frame, and an indicator for indicating a section to be processed. Accordingly, pre-finding or detecting the format of an input image is required for accurately obtaining the vertical retrace blanking period and process thereof for accurately processing the subsequent operations, which requires lots of components and increases the design complexity.
Therefore, it is desirable to provide an improved device to mitigate and/or obviate the aforementioned problems.